Methods and apparatus for detecting abnormalities in proximity effect heat-tracing circuits

Claim 1

Apparatus for detecting current flow abnormalities in either of a pair of proximity-effect pipeline heat-tracing circuits for heating at least two serially connected pipeline sections, comprising: a first source of alternating current for heating one of said pipeline sections; a second source of alternating current for heating the other of said pipeline sections, said second source having the same voltage phase as said first source and having one output terminal connected to one output terminal of said first source to form a current node; a first proximity effect heat-tracing segment in heat-exchange relation with one of said pipeline sections, said first segment including a first elongated insulated conductor extending through and surrounded by a first heat tube, said first heat tube having one end connected to said node and the other end connected to one end of said first insulated conductor; a second proximity effect heat-tracing segment in heat-exchange relation with the other of said pipe sections, said second segment including a second elongated insulated conductor extending through and surrounded by a second heat tube, said second heat tube having one end connected to said node and the other end connected to one end of said second insulated conductor; a single current transformer having (1) a first conductive element connected between said first alternating current source and the other end of said first insulated conductor extending through said first heat-tracing tube segment and (2) a second conductive element with opposite polarity to said first conductive element connected between said second alternating current source and the other end of said second insulated conductor extending through said second heat-tracing tube segment, and (3) a third conductive element inductively coupled to both said first and said second conductive elements; and means for detecting current flow induced in said third conductive element by any difference between the currents flowing through said first conductive element and said second conductive element whereby abnormal current flow and unequal generation of heat in one of said heat-tracing segments relative to the other of said heat-tracing segments is detected by said current flow.

Claim 14

A method for detecting current flow abnormalities in either of a pair of proximity-effect pipeline heat-tracing circuits for heating two serially connected pipeline sections comprising a first heat-tracing segment capable of carrying a first current to heat one of said pipeline sections by heat exchange therewith, said first segment including a first heat tube having a first insulated conductor extending therethrough and further comprising a second heat-tracing segment capable of carrying a second current to heat the other of said pipeline sections by heat exchange therewith, said second segment including a second heat tube having a second insulated conductor extending therethrough comprising the steps of: passing an alternating current from one source through a first conductor traversing a window of a single window-type current transformer to said first insulated conductor extending through said tube of said first heat-tracing segment; passing an alternating current from a second source through a second conductor traversing the window of said single window-type current transformer to said second insulated conductor extending through said tube of said second heat-tracing segment coupling said second conductor and said first conductor so that current flow in said second conductor is opposite in polarity with respect to current flow in said first conductor; connecting in common one of the terminals of said first current source with one of the terminals of said second current source and connecting both of said terminals to an end of both said first and said second heat-tracing segment tubes, said ends being remote from the connection between the end of each of said insulated conductors and the other end of each of said heat-tracing tubes; and detecting a current flow induced in a winding of said window-type current transformer as an indication of abnormal current flow in one of said heat tracing segments relative to the other segment.

Claim 15

A method for detecting current flow abnormalities in either of a pair of proximity-effect pipeline heat-tracing circuits for heating two serially connected pipeline sections comprising a first heat-tracing segment capable of carrying a first current to heat one of said pipeline sections by heat exchange therewith, said first segment including a first heat tube having a first insulated conductor extending therethrough and further comprising a second heat-tracing segment capable of carrying a second current to heat the other of said pipeline sections by heat exchange therewith, said second segment including a second heat tube having a second insulated conductor extending therethrough comprising the steps of: passing an alternating current from one source through a first conductor traversing a window of a single window-type current transformer to said first insulated conductor extending through said tube of said first heat-tracing segment; passing an alternating current from a second source through a second conductor traversing the window of said single window-type current transformer to said second insulated conductor extending through said tube of said second heat-tracing segment coupling said second conductor and said first conductor so that current flow in said second conductor is opposite in polarity with respect to current flow in said first conductor; connecting in common one of the terminals of said first current source with one of the terminals of said second current source and connecting both of said terminals to an end of both said first and said second heat-tracing segment tubes, said ends being remote from the connection between the end of each of said insulated conductors and the other end of each of said heat-tracing tubes; and detecting a current flow induced in a winding of said window-type current transformer as an indication of abnormal current flow in one of said heat tracing segments relative to the other segment.

Claim 17

A method for detecting current flow abnormalities in either of a pair of proximity-effect pipeline heat-tracing circuits for heating two serially connected pipeline sections comprising a first heat-tracing segment capable of carrying a first current to heat one of said pipeline sections by heat exchange therewith, said first segment including a first heat tube having a first insulated conductor extending therethrough and further comprising a second heat-tracing segment capable of carrying a second current to heat the other of said pipeline sections by heat exchange therewith, said second segment including a second heat tube having a second insulated conductor extending therethrough comprising the steps of: flowing an alternating current from a first source through a first primary winding of a single dual primary current transformer to an insulated conductor extending through said first heat-tracing segment tube; flowing another alternating current from a second source through a second primary winding of said single dual primary current transformer to an insulated conductor extending through a second heat-tracing segment tube; coupling said second primary winding and said first primary winding so that current flow in said second primary winding is opposite in polarity to current flow in said first primary winding; connecting one terminal of said first current source to one terminal of said second current source and in common with the end of both said first and said second heat-tracing segment tubes and opposite to the ends of said segment tubes connected to the opposite end of the respective insulated conductors connected to said first and second primary windings, and detecting a difference between the first and second primary winding currents induced in a secondary winding of said dual primary current transformer to indicate abnormal current flow in either of said heat-tracing segments relative to the other segment.

Claim 18

A method for detecting current flow abnormalities in either of a pair of proximity-effect pipeline heat-tracing circuits for heating two serially connected pipeline sections comprising a first heat-tracing segment capable of carrying a first current to heat one of said pipeline sections by heat exchange therewith, said first segment including a first heat tube having a first insulated conductor extending therethrough and further comprising a second heat-tracing segment capable of carrying a second current to heat the other of said pipeline sections by heat exchange therewith, said second segment including a second heat tube having a second insulated conductor extending therethrough comprising the steps of: flowing an alternating current from a first source through a first primary winding of a single dual primary current transformer to an insulated conductor extending through said first heat-tracing segment tube; flowing another alternating current from a second source through a second primary winding of said single dual primary current transformer to an insulated conductor extending through a second heat-tracing segment tube; coupling said second primary winding and said first primary winding so that current flow in said second primary winding is opposite in polarity to current flow in said first primary winding; connecting one terminal of said first current source to one terminal of said second current source and in common with the end of both said first and said second heat-tracing segment tubes and opposite to the ends of said segment tubes connected to the opposite end of the respective insulated conductors connected to said first and second primary windings, and detecting a difference between the first and second primary winding currents induced in a secondary winding of said dual primary current transformer to indicate abnormal current flow in either of said heat-tracing segments relative to the other segment.